Generally, scroll rotors are applied to scroll compressors for vehicles or air conditioners. Scroll rotors have high cooling efficiency and little vibration noise, and can be used together with a substitute refrigerant. In addition, scroll rotors can reduce the volume of air conditioners due to the small size of compressors. Furthermore, a refrigerant gas leaks little and that either torque or load changes little. Due to these advantages, scroll rotors are widely used.
A wrap part of a scroll rotor is characterized in that it has a complicated and asymmetric shape since a spiral curve is formed around the central portion of the scroll. When a scroll rotor is fabricated using a typical forging process, the wrap part is not molded with even height. Post machining for reducing the unevenness of the height is thus required and a considerable amount of material is lost, thus reducing economic competitiveness, which is problematic.
As another approach for making the height of the wrap part to be even, closed-die forging was proposed. However, there are problems in that a molding load may rapidly increase at a final molding step, thereby damaging a mold and increasing danger to workers.
On the other hand, as a further approach for minimizing the unevenness of the height of the wrap part and reducing the amount of post machining, proposed was a method of molding a scroll rotor using back pressure. However, this method also has the following problems: (1) a separate hydraulic power supply for providing back pressure is required, and a molding load is increased by the back pressure; (2) bulging in the wrap part caused by the back pressure increases the contact pressure between the wrap part and the mold surface in an extrusion section, making it difficult to withdraw a molded product after molding is finished; and (3) additional maintenance for separate back pressure equipment is required.